The American Society for Emergency Contraception (ASEC) recently held their annual EC Jamboree in Washington, DC. Participants included health care providers, researchers, reproductive health advocates, and pharmaceutical stakeholders.
One highlight was the key clinical discussions centered on drug interactions between emergency and other hormonal contraceptives, including ulipristal acetate (ella, Afaxys Pharma).
A selective progesterone receptor modulator, ulipristal acetate binds the progesterone receptor, and has both antagonistic and partial agonistic effects. When ulipristal acetate is in the picture, along with another progestin hormone, there will be competition for the progesterone receptors. For this reason, the patient’s use of another progestin-containing hormonal contraceptive either before or after may impact its effectiveness 
This theory is based on the pharmacology of the drugs and was supported by a European study. The study looked at the impact of starting a desogestrel progestin-only pill the day after taking ulipristal acetate, compared to starting the same progestin-only pill without ulipristal acetate beforehand. The group that had taken ulipristal acetate showed a slower onset of action of the progestin-only pill in preventing ovulation and thickening the cervical mucus. This particular progestin-only pill is not available in the United States 
Following this study, Afaxys revised the ulipristal acetate label in March 2015 to include: “Hormonal contraceptives: Progestin-containing contraceptives may impair the ability of ella to delay ovulation … Avoid co-administration of ella and hormonal contraceptives. If a woman wishes to start or resume hormonal contraception after the intake of ella, she should do so no sooner than 5 days afterwards, and she should use a reliable barrier method until the next menstrual period.“ 
Last year, another study found that combined oral contraceptives containing estrogen and progestin hormones are expected to reduce efficacy of ulipristal acetate, as well. In this United States study, researchers evaluated the impact of initiating an ethinyl estradiol/levonorgestrel combined pill 2 days after ulipristal acetate use . More participants experienced ovulation when the combined pill was initiated compared to those who did not initiate any hormones after ulipristal acetate.
Pharmacists and pharmacy staff can refer to a 1-page guide created by ASEC, available on the organization’s website at americansocietyforec.org, for additional information on FDA-approved emergency contraceptives.
- Brache V, Cochon L, Duijkers IJ, et al. A prospective, randomized, pharmacodynamic study of quick-starting a desogestrel progestin-only pill following ulipristal acetate for emergency contraception. Hum Reprod. 2015;30(12):2785-2793.
- Ulipristal acetate (ella) prescribing information. May 2018. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=052bfe45-c485-49e5-8fc4-51990b2efba4
- Edelman AB, Jensen JT, McCrimmon S, Messele-Forbes M, O’Donnell A, Hennebold JD. Combined oral contraceptive interference with the ability of ulipristal acetate to delay ovulation: A prospective cohort study. Contraception 2018;98(6):463-466.
This article was originally published in Pharmacy Times.